Transmission repeating system for radio and carrier telegraph systems



Jan. 8, 1929. 1,697,903

` R. H. CLAPP TRANSMISSION REPEATING SYSTEM FORA RADIO AND CARRIER TELEGRAPH SYSTEMS www ALMA

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ROBERT H. CLAPP, OF IXIIOHIMOII'ID HILL, NEW YORK, ASSIGNOR TO `AMERIICAN' TELE- IPHONE .AND TELEGRAPH COMPANY, A CORPORATION OF NEW .YORIK 4 'mei-remission iinraarrirue-ssz's'iiiifi Fon RADIO Ann CARRIER TELEGRAPH SYSTEMS.

Application filed August 18, 1926. Serial No. 130,067.

Thisinvention relates to4 `a transmissionregulating system for radio and carrier telegraph systems, and particularly'tto a system of the type in Which'the gain of the amplifier is varied by and in accordance with changes`inV the signaling current itself to compensate'for changes in the line characteristics.

In high Lt'requency telegraph systems, which term is intended to include both radio and carrier systems, it has been customary to empl-oy means for automatically changing the gain` of the ampliiei's in the circuit. to compensate for changes in its transmission equivalent. Heretoi'ore it has been cus*- tomary to transmit a control current consisting of a single frequency, lying outside of the band of signaling frequencies, and to utilize this control current to operate the regulating device, by means of which the amplitier gain is varied. This control current, which is termed in the art a pilot channel, utilizes a portion of the frequency spectrum -that might otherwise be employed for the transmission of signals.' Consequently, if the regulation of the ampliiier gain can be effected by changes in the signal voltagesA themselves, the use of a. pilot channel is rendered unnecessary a-nd a savingpWill result.

In the copending application of R. W. Deardori, Serial No. 138,977, filed Oct. l, 1926, there is described a system by means 'of Which theampliier gain of a radio or o carrier telegraph system may be varied in accordance With changes in the voltage of the signaling channels themselves to co mpensate *for changes in the transmission equivalent of the system, the regulator utilizing three vacuum tubes Which are acted upon by the signal voltage itself, which tubes serve to operatea gain control device in the input of the amplifier.

The present invention is a modilication of D that disclosed by Deardorf, and consists in effecting the control of the amplifier gain by means of a regulator requiring only tWo vacuum tubes.v

Other objects of this invention will be apparent from the following description, when read in connection With the attached drawing, of Which lFigure l shows schematically a simple form of embodiment of the invention, and Fig. 1a is a graph illustrating-- the principle underlying the invention.

In Fig. l the transmittingapparatus 1 is connected With the line L1 in order to transmit thereover carrier telegraph signals.

This transmitting apparatus may be of any'y Well-known type for producing carrier'signals in Which a marking impulse consists of and 30. The voltage applied to the said grids by the potentiometer may be varied by movement of its contact point, which is controlled by the arm 12 of a gain control de- `vice 6. This device,.which isshovvn schematicall-y in the drawing, is a modification of a Leeds and N orthrup recorder described in the patent to Leeds, 1,125,699, dated January y 19, 1915, the modification consisting in the replacement of the pen which is normally employed for the production vof a record, with a contact point engaging the Wire of the potentiometer. This type of electrical recorder is also described in Bulletin No. 871, of the Leeds and N orthrup Company, published in 1,921. In an arrangementof that type the flow of current through the coil 11 in a given direction Will cause the arm 12 to move in a definite direction, and the magnitude of its motion will be dependent upon -thestrength of the current in the coil. Like- Wise a reversal of the current.l through the coil 11 will cause the arm 12 to move in the' opposite directionl The plate circuit of the tube 3, which effects rectification and amplitlcationA of the marking impulses, extends from the grounded battery 20 throughv the Winding 25 of relay 21 and throughthe shunt 23, thence through the Winding of relay 4 to the plate of the tube. Relay 4 serves to transmit the rectified impulses over the line L2 to the direct current telegraph apparatus 2 connected therewith. The plate circuit of the tube 30 extends from. the grounded battery 20 through the Winding 22 to the plate of that tube. The armature of relay 21 is connected through the retardation coil 29 With one side of the operating WindeoA by virtue of'whichit is possible to effect regand 27. The arrangement is such that when the armature o relay 21 is upon one contact, current will flow through the winding 11 in' such direction-as to cause thev arm l2'to move ina' predetermined direction, and when. thearmatureof relay 2l moves to its other contact, current through the winding 11 will be reversed and the arm l2 will move inthe opposite direction.

The principle underlying thisinvention,

ulation of thegain control device by means of two vacuum tubes, will be clearly seen by referring to Fig; l, which represents the well-known relationship between the grid voltage and the platecurrent of a vacuum tube. From this figure' it will be seen that tube 8 has a different characteristic fro1n` tube 30. In this invention the grid biasing voltages of the tubes have been so chosen as to. cause the characteristics to cross-at some fixed voltage. It is, of course, bvious that at the point where the characteristics cross, the same plate currents flow in the output circuits of the tubes, each of which includes a Winding of the polar relay. The winding 25 is shunted by the resistance 23 sothat the ilux produced by the current through that winding will be equal `and opposite to that produced by the current in the winding 22 when the normal signal is applied to the grids of tubes 3 and 30.v Thevresult of this is that for the normal signaling voltage the armature of the relay 21 will be unaffected and the gain control device 6 will remain unope'rated. If the signal voltage decreases below normal, the plate currentthrough the winding 22 of tube-30 will be greater than that through the winding 25 of tube 3, asl will be readily seen vin Fig. la. Consequently, the armature of relay 2l will be moved to one of its contacts, which will cause current to iiow through the winding 11 and the arm 12 will be moved in such a direction as to increase the voltage applied to the grids of the tubes 3 and 30. As soon as Lthe voltage applied to the grids is equal to y of Fig. la, the armature 21 will be restored to its normal midposition by virtue of the equal opposing luxes produced bythe windings 22 and 25. On the other hand, it' the signaling voltage is greater than the normal value, y, the current through the winding 25 will be greater than that through sented by y of Fig. 1.

the winding 22. This will cause the armature'21 to-move to its other contact, which will cause current to iiow through the winding 11 so as to move the arm l2 in such dithe voltage applied to the-grids of the tubes 3 and 30 to that repre lWhen this condition exists the armature of relay 21 will again return to its normal midposition.

lt will belseen that by means of the rangement shown and described above,

arthe pression of such `with the said source,

the relay 4 which controls the transmission of the rectified impulses over the line L2, may be kept substantially constant regardless of variations in the transmission equivalent of the line L1 over which the high :tr uency telegraph impulses are transmitted. dit will further be seen that by using vtubes having grid voltageplate current characteristicsthat cross at a predetermined grid voltage, it is possible to effect complete regulation of the gain control device by an arrangement employing only two vacuum tubes. i

This invention has plied to atc'arrier telegraph system, but it 1s, of course, obvious cable to a radio systcm since the transmitvting device l' may be connected -with a sending antenna, and the potentiometer 5 may be bridged across a receiving antenna. Accordingly, wherever the term high frecurrent applied to that it is equally appli quency telegraph impulses has been veinployed, it should be understood to ycover either afcarrier or a radio system.

While the invention has' been disclosed as embodied in a particular form, it is capable of embodiment in other forms without de parting l:from the spirit and scope of the appended claims.

What is claimed is: 1. In a telegraph system in which a mark is transmitted by a train of waves of fixed normal amplitude and a space by the supwaves, or'vice versa, the combination. with a source of alternating current of two vacuum tube rectifiers having their input circuits connected in parallel with the said source, the said tubes having dissimilar grid voltage-plate current characteristics such that the plate currents of both tubes will be equal when the normal alternating voltage is applied to the'grids of both tubes and will be unequal or all other values of grid voltage, means to apply a voltage tothe plates of the said tubes, an electro-responsive device having a winding individual to each plate circuit, the windings bein oppositely poled, and means controlled y the said electro-responsive means to vary the input voltage of the said tubes inversely with changes in the plate currents.A

2. In a telegraph system in which a mark is transmitted by a train of waves of fixed normal amplitude and a space by the suppression of such waves, or vice versa, the -combination with a source vof alternating iml current of two vacuum'tube rectiiers having their input circuits connected in parallel the said tubes having dissimilar grid voltage-plate current characteristics, means to negatively bias the grids of both tubes, the degreeof bias ot one tube being dierent from di`erence being such,l that' the plate cur rents ot both tubes will-'loe equal 'when the that ot the other, the

` the input of the' said normal alternating voltage is applied to the grids thereof and Will be unequal for all other values of grid voltage, means to apply a plate potential tothe said tubes, an electrorespo'nsive device having a Winding individual to each plate circuit, the windings being oppositely poled, and lmeans controlled the said electro-responsive means to vary device inversely with changes in the plate currents.

3. In a telegraph systemin which a mark transmitted by a train of Waves of iiXed normal'amplitude and a space bythe suppression of s uch Waves or vice versa., the combination. with a 'source of alternating current of two'vacuum tube rectifiers having their input circuits connected in parallel with the said source, the said tubes having dissimilar grid voltage-plate current characteristics, means to negatively bias the grids of both tubes, the degree of bias of one tube being different from that of the other,the difference being such that the plate currents of both tubes Will be equal when the normal alternating voltage is applied to the grids thereof and Will be une' qual for Vall other values Aof grid voltage, means to' apply a plate potential to the said tubes, an electroresponsive device having a Winding individual to each plate circuit, the windings being oppositely poled, a regulating device controlled by the saidelectro-responsive device, and a potentiometer controlled by 'i the said regulating device to vary the input voltage of the said tubes inversely With changes of the plate currents.

4( In a'carrier telegraph system, the combination with a source of alternating current of a transmitting medium over or through which the said currentmay be transmitted and a receiving circuit upon Which said current may be impressed, said circuit comprising a plurality of thermionic recti-,

fiers having dissimilar current characteristics, tively the grids of said tubes to such degree that for' the normal received alternating voltage the plate currents of both rectifiers grid voltage-plate means to bias nega- Willbe of the same magnitude, an electro.

being arranged to restore the input voltage I of said rectiiers to normal. l.

In testimony whereof, I have signed my name to this specication this 17th day of i August, 1926.

ROERT H. CLAPP. 

